This invention pertains to a process to clean a polymeric article, such as a polyurethane glove, so as to remove non-volatile residues and low-volatility residues from the article. The process employs a bath consisting essentially of a suitable solvent at an elevated temperature of approximately 60xc2x0 C.
Polyurethane gloves are used in clean rooms, in which microelectronic devices requiring strict control of cleanliness are handled. Polyurethane gloves made from LYCRA(copyright) by dip-forming and curing on glove forms are available commercially from Wilshire Technologies, Inc. (xe2x80x9cWilshirexe2x80x9d) of Carlsbad, Calif. LYCRA(copyright) is a trademark registered by E.I. DuPont de Nemours and Company (xe2x80x9cDuPontxe2x80x9d) of Wilmington, Del., and licensed to Wilshire for a DuPont brand of polyurethane, which, as used by Wilshire to make polyurethane gloves for such use, conforms to the following specifications:
Percent solids, 18.5%xc2x10.5%;
40xc2x0 C. falling ball viscosity, 175 poisexc2x125 poise;
Intrinsic viscosity, 1.1 poisexc2x10.1 poise; and
TiO2, 3.5%xc2x10.3%.
Polyurethanes including LYCRA(copyright), supra, tend to comprise, in any given batch used for dip-forming of gloves or other articles, fractions of low, intermediate, and high molecular weights. Notoriously, polyurethane fractions of low molecular weights tend to form excessively high levels of low-volatility residues, which detract from cleanliness of dip-formed articles, such as dip-formed gloves. Therefore, despite polyurethanes having other characteristics favoring their use for gloves for clean rooms, their use for gloves for such use has been inhibited.
Commonly, a sample glove from a batch of polyurethane gloves intended for such use is tested for cleanliness by immersing the sample glove from the batch, in a quiescent bath consisting essentially of a solvent selected from isopropyl alcohol, hexane, acetone, and blends of isopropyl alcohol and hexane, at ambient temperature, for a predetermined time. Varying from one prospective user to another, the predetermined time may be as short as approximately twenty minutes, or as long as approximately twenty-four hours. After the predetermined time, the sample glove is withdrawn from the bath and all volatiles are evaporated from the batch, so as to leave non-volatile residues and low-volatility residues, which may include oils, waxes, and polyurethane fractions of low molecular weights. The non-volatile and low-volatility residues from the batch are weighed collectively. If their collective weight exceeds a predetermined tolerance, the batch is rejected.
Commonly, gloves for clean rooms are cleaned with deionized water, which removes only surface contaminants. Cleaning of such gloves with deionized water does not deliver such extremely low levels of non-volatile and low volatility residues as users demand.
Commonly, gloves for clean rooms are washed with a washing solution, in a commercial washing machine. Because much of the washing solution becomes trapped within the washed gloves, it becomes costly, difficult, and time-consuming to dry such gloves.
Alternatively, gloves for clean rooms are cleaned with a solvent, such as isopropyl alcohol, in a commercial dry-cleaning machine, in which much of the solvent becomes trapped within the washed gloves. In such a machine, the temperature must be maintained at a safe level below the flash point of the solvent. Drying of isopropyl alcohol and other solvents having low flash points requires costly explosion-proof equipment.
This invention provides a process to clean a polymeric article so as to remove non-volatile residues and low-volatility residues from the article. Broadly, the process comprises immersing the article in a bath consisting essentially of isopropyl alcohol, at an elevated temperature of approximately 60xc2x0 C., for a predetermined time not less than approximately five minutes, preferably for a predetermined time of approximately ten to twenty minutes, withdrawing the article from the bath, and drying the article, as by allowing the article to be air-dried.
The process provided by this invention can be effectively employed to clean a polymeric article, as cured on a form, before the article is removed from the form. Thus, the process provided by this invention comprises immersing the form bearing the article in a bath consisting essentially of a solvent selected from isopropyl alcohol, hexane, and blends of isopropyl and hexane, at an elevated temperature of approximately 60xc2x0 C., for a predetermined time not less than about five minutes, preferably for a predetermined time of approximately ten to twenty minutes, withdrawing the form bearing the article from the bath, and drying the article on the form, as by allowing the article to be air-dried on the form.
Although the process provided by this invention is intended particularly to clean polyurethane gloves for use in clean rooms, the same process is expected to be also useful to clean polyurethane gloves for use in pharmaceutical manufacturing facilities, or for use in medical or surgical facilities, to clean other polyurethane products, such as finger cots and condoms, and to clean gloves and other products made from polymers other than polyurethanes, e.g., acrylonitrile or natural latex.
Although the bath may be quiescent or agitated, it is preferred for the bath to be agitated, either mechanically or via bubbling of air or another gaseous medium that is inert relative to the bath.